A three-dimensional tapered waveguide is disclosed for planar lightwave circuits. More specifically, a three-dimensional tapered waveguide is disclosed which is fabricated using two reactive ion etching RIE processes which result in a positive RIE lag affect and a reverse RIE lag affect to create a tapered optical waveguide which has a width and depth at one end that are both greater than the width and depth at a second opposite end.
Optical communication systems play an important role in the transmission and processing of data. Due to the large bandwidth of an optical glass fiber, several signals can share the same optical fiber and high transmission rates can be obtained. Thus, in addition to long distance transmission systems, optical fibers also play an important role in advanced computer network and electronic systems.
When using optical fibers in computer and electronic applications, data is transmitted through an optical fiber which, in turn, transmits the data to an optical device (e.g., an optoelectronic device). This optical device is connected or coupled to one or more optical fibers. At the point of coupling, it is extremely important to obtain an efficient coupling or transfer of light between the optical fiber and the optical device. To provide an efficient coupling, the refractive indices of the optical fiber and the optical device must be closely matched. Specifically, a difference in the refractive indexes of the optical fiber and the optical device can result in loss of the optical signal. This problem is also compounded by geometrical differences between the end of the optical fiber and the input end of the optical device.
To solve the geometric mismatch problem, a number of approaches have been attempted. Such approaches include the use of micro lenses and tapered fibers. These approaches have proven unsatisfactory, however, because these solutions present alignment problems resulting in high packaging costs.
Another approach is to insert a separate optical waveguide module between the fiber and the optical device. Although relatively sufficient mode-matching and high coupling efficiencies can be obtained with such modules, small alignment tolerances between the fiber and the optical device hinder efficient and low-cost packaging.
Therefore, the industry has concentrated on the integration of an optical waveguide in the optical device. However, appropriate matching of the input end of the optical waveguide and the optical fiber still remains a problem. Specifically, typical fiber optic cables have a circular cross section with a diameter ranging from 8.2 xcexcm to 9 xcexcm. The typical optical waveguide has an input end that does not have a circular cross section and has a width ranging from 2 xcexcm to 8 xcexcm. Thus, most waveguides do not provide a suitable match between the width of the waveguide and the diameter of the optical fiber. The difference in geometries between the optical fiber and the optical waveguide results in additional mode mismatch between the optical fiber and the waveguide. As a result, coupling loss occurs which results in poor data transfer and increased power requirements.
Further, because the optical waveguide couples a relatively large optical fiber to a relatively small optical device, the input end of the optical waveguide must be larger than the output end. Thus, a tapering of the waveguide between the input and output ends is required. Technology is available to provide a lateral taper but this approach only changes the width of the waveguide without affecting the height of the waveguide. Thus, a geometric mismatch between the fiber and the waveguide still exists. Other technology involves the use of vertical tapers but, because the width is not tapered, a geometrical mismatch still exists.
Attempts at combining vertical and lateral tapering have been attempted. However, the technologies available require multiple process steps that include different etching processes such as wet etching, dip-etching, dynamic etch mask techniques, stepped etching and diffusion-limiting etch techniques. The combination of these varying and different etching techniques to fabricate a single device is slow and therefore costly. Other tapered waveguides can be fabricated using epitaxial growth techniques which require multiple steps, are slow and also costly.
Therefore, there is a need for an improved method for fabricating three-dimensional tapered waveguides on planar light wave circuits that is easier and less costly than the processes described above which require multiple and different processing steps.
An improved method for fabricating three-dimensional optical waveguides in a planar lightwave circuit is disclosed.
An improved three-dimensional tapered waveguide incorporated into a planar lightwave circuit is also disclosed.